Apparatus for post-exposure treatment of lithographic plates

ABSTRACT

Apparatus for post-exposure treatment of lithographic plates comprising a horizontal endless belt for transporting a lithographic plate successively to, through and past a series of operating stations. The apparatus includes a carriage at one of the stations mounted above the belt for reciprocating movement transverse to the belt, rubbing members rotatably carried by the carriage for rubbing developing composition onto the lithographic plate as it is transported on the belt, and a mechanism movable with the carriage for rotating the rubbing members as the carriage is reciprocated.

SHEET 2 [If 5 PATENTEDms' 8 m2 SHEET '4 BF 5 FIG,4

' 1 APPARATUS FOR POST-EXPOSURE TREATMENT OF LITHOGRAPHIC PLATESCROSS-REFERENCE TO RELATED APPLICATION This application is acontinuation of our application Ser. No. 745,736, filed July 18,abandoned.

The invention relates to process and apparatus for post-exposuretreatment of lithographic plates to pressready condition by the additiveprocess, and the apparatus aspect thereof represents a compact,simplified, and within limits, more economically operatable improvementupon the apparatus disclosed in the copending application of Harrell,Essmueller and Bax, Ser. No. 729,040, filed May 14, 1968, now US. Pat.-No. 3,608,464.

One object of the invention is to expedite the postexposure treatment oflithographic plates, and to minimize the consumption of chemicalsutilized in such treatment.

Another object of the invention is to provide an apparatus forperforming automatically the post-exposure treatments of such plates,and to reduce the consumption of materials employed in such treatments.

A further object is to provide an apparatus which is more economical tomanufacture and to operate than that disclosed in the aforesaidapplication of Harrell et al copending 1968, now

These and other objects of the invention, which'will become apparent tothe skilled in the art as the description proceeds, are accomplished byproviding a process and machine wherein the exposed lithographic plateis moved continuously to, through and beyond, stations at each of whichone of the steps of the process is performed. Such steps include: (1)depositing metered quantities of developer composition upon the activesurface of the plate; (2) spreading the developer composition over theactive surface of the plate and rubbing it with a compound motion whichinvolves both circular and rectilinear components, each in pluraldirections, while the volatile components of the developer compositionare being evaporated; (3) washing away with water all of the developerwhich has not adhered to the light-struck areas on the active surface ofthe plate; (4) at least partially drying the active surface of theplate; (5) depositing measured quantities of a preservative compositionupon the plate and (6) spreading the preservative composition over, andrubbing it on, the plate.

Such continuous movement of the plate undergoing treatment isconveniently accomplished by transporting the plate on an endless belt.The endless belt is preferably smooth enough and held flat enough thatwhen a thin flexible sheet of metal, such as a common lithographicplate, is laid upon it, air is excluded from the interface, and the twostick together so long as substantially flat coincidence is maintained,an action which is facilitated if either contacting face is damp with aliquid which, at least to some extent, wets both. Accordingly, the beltis preferably made of a material which is, at least to some extend,phillic to liquids which are phillic to the reverse (non-active) surfaceof the plate, and the belt is preferably of a material, for exampleneoprene, which may be vulcanized into endless condition in situ, i.e.,while trained around one or more drive-, or guide-, rollers. While sucha belt should be with the present invention, by providing a continuouslycirculating pressurized system for supplying the developer liquid inmetered quantities to a plate, and immediately thereafter to subject theplate to the action of a plurality of rotating rubbing heads which aretranslated, transversely of the direction of plate movement, whilewhirling about their own axes, at a speed sufficient to induce aircirculation of a character to accelerate the evaporation of at leastpart of the liquid components of the developer from adjacent incrementsof the plates active surface. Each head is equipped with a rubbingmember which is essentially porous, non-abrasive and possessed of atleast enough resiliency to compress, albeit slightly without permanentdeformation. The rubbing members may have some, but preferably little,absorptivity toward the viscous developer. Any natural or syntheticsponge may be used as a rubbing member, but it is preferable that it beone whose average pore size is large, such as the so called coarse graincellulose sponge of commerce. The coarse grain sponge is characterizedby the fact that many of its pores are a quarter inch or more indiameter, the average pore size being greater than three-thirty-secondsof an inch with relatively few as small as one-thirty-second inch, asdistinguished from fme grain sponges whose pores are predominantly onthe order of one-thirty-second inch in diameter, and, according tocommercial practice, must be no greater than three-thirty-seconds of aninch.

The several rubbing members are preferably mounted in a cluster so thattheir respective axes of rotation are parallel and spaced apart adistance approximating the diameter (or diagonal) of the individualrubbing members. Preferably, the rubbing members are arranged in pairswith the individual members of a pair rotating in opposite senses sothat, at the bight where their respective peripheries closely approacheach other, both are moving in the same general direction which may beeither parallel with, or transversely of, the direction of movement ofthe endless belt. A cluster of two pairs of rubbing members isdesirable, so that one pair (herein termed the leading pair) has itsbight motion addressed in the direction of plate and belt movement,while another pair (herein termed the trailing pair) addressed counterto the direction of plate and belt movement. The invention contemplatesthat the developer be deposited upon a plate on the moving belt at aposition ahead, and preferably immediately ahead, of the leading pair ofrubbing members. Preferably, the developer is deposited by dropping itin metered quantities from an outlet substantially aligned, in thedirection of plate movement, with the bight between the leading pair ofrubbing members, and as close as practical thereto.

in accordance with the present invention, the respective rubbing membersare maintained, during operation, under slight, but substantiallyuniform, compression, e.g., enough to compress a coarse grain cellulosesponge normally one inch thick to a thickness of about seven-eighthsinch. While under such compression, and with an exposed lithographicplate moving thereunder, the respective rubbing members are moved with acompound motion, in rotation about their own axes, and in translationcrosswise of the endless belt, and at right angles to the direction ofbelt movement. Hence, the relative movement between a pair of rubbingmembers and a plate undergoing movement involves not only relativerotation in opposite senses, but also relative translation in tworectilinear directions.

The rectilinear translation crosswise of the belt is achieved bymounting the cluster of rubbing members upon a carriage which isreciprocated in the crosswise direction with a stroke whose amplitudepreferably exceeds the width of the belt, so that at least part of eachrubbing member will overhang the edge of the endless belt at one end orthe other of the reciprocatory stroke. Thus, the edge of the belt actsas a scraper blade to remove excess developer from that or those rubbingmembers which will be trailing, in the reciprocatory respect, on theimpending stroke. In spite of the fact that such imposes a practicallimit upon the widthwise (of the belt) dimension of a plate beingtreated, it is preferred that the frequency of reciprocation of therubbing carriage be so coordinated with the speed of the endless belt,that the plate move longitudinally no more than about a diameter (ordiagonal) of a rubbing member while the rubbing carriage is makingacomplete cycle of reciprocation transversely of the direction of platemovement in the belt. Hence, the lineal speed of the rubbing carriagemust be substantially greater than the lineal speed of the belt.

In order to minimize the time consumed in reversing the carriage stroke(twice during each complete cycle of reciprocation) and to minimize themechanical shock involved in such reversals, the invention contemplatesa carriage drive mechanism which, during operation, moves continuouslyin the same direction and remains constantly in engagement with thecarriage. The latter is accomplished by an endless chain and sprocketdrive in which one chain-link or -pin is so connected inforce-transmitting relationship to the carriage that, at each end of areciprocatory stroke, the carriages rate of deceleration to zerovelocity, and its rate of acceleration from zero to the chordal velocityof the chain, is the same as that undergone by any chosen point on thechain as it reverses direction in moving about a sprocket at an endloop, to wit, but for mechanical looseness, like the trigonometricfunction versine decreases from a maximum to zero, and then increases tothe maximum as a radius moves from one end of a diameter to the otherend of that diameter.

To transmit motive force from the chain to the carriage, the chosenchain-link or -pin is connected to the carriage by means whichaccommodates relative motion (between the chosen link or pin and thecarriage) in' the direction perpendicular to a plane which includes thefixed axes of both sprockets. Thus, when the axes of the sprockets arehorizontal, the aforesaid relative motion is vertical; and, when theaxes of the sprockets are vertical, the relative motion is horizontal.One of the chain and carriage may have an affixed raceway, while theother has an affixed follower caged inthe raceway; and the racewaypreferably has a length sufficient to accommodate movement of thefollower between opposite extremities of the sprockets pitch circlediameter. The latter, while not imperative, reduces mechanical strain onthe follower.

The same reciprocatory drive may also motivate a reciprocating rubbingmember at the preservative station of the apparatus, and, if desired,may, through a rack and pinion, impart rotary motion to one or more suchrubbing members.

After an increment of a plate moving with the endless belt has departedfrom the region of operation by the developer rubbing members, theactive surface of theplate is subjected to a spray of water which erodesand washes from the plate passing therebeneath all of the loosematerial, solid and liquid, of the developer which has not, during thepreceding treatments, become adhered to the light-reacted areas of theplate. Beyond the water spray station, a wiping member of the squeegeetype makes water-sealing engagement against the active surface of theplate. Such a squeegee may be either a roller or a blade, in eitherevent having a contacting part of rubber, or other relatively softmaterial, which makes a substantially watertight seal with the platetraveling therebeneath. Thus unsorbed and flowable water on the activesurface of the plate is wiped off as the belt moves the plate under thesqueegee, and such-water is drained sidewise off the belt, as by tiltingthe belt at that region; and any tendency for such water to flow,counter to the belt movement, back into the developer station may beovercome by tilting the apparatus, or at least that region of the belt,so that gravity prevents such counterflow.

Beyond the last-mentioned squeegee, the plate passes to a preservativestation under another rubbing member, which may be of like character tothose previously mentioned, but not necessarily so because thepreservative composition usually requires less rubbing then does thedeveloper composition. Prior to passing under the preservative rubbingmember, there is dropped upon the dewatered moving plate meteredquantities of the preservative composition. As at the developer station,one, or a series of spaced metering devices is arranged so as to dropthe requisite quantity (usually less than that of the developer) of thepreservative composition upon the subjacent plate. The

- preservative composition then undergoes rubbing of and organic solventas may remain entrained in the residual preservative after thelast-mentioned squeegeeing. On the other hand, where it is desired toaccumulate plates emerging from the apparatus by stacking them one uponthe other, it is advisable to expedite the evaporation of water andorganic solvent as by passing the plates individually through anysuitable dryer before they are stacked.

The series of post-exposure treatment operations requires an elapsedtime which is but a small fraction of that required when the operationsare carried out by hand, and the drying aspect of the developmentoperation, as well as that of the preservative application, is expeditedby the air circulation induced by the motion of the several rubbingmembers.

One form of apparatus embodying the inventions is disclosed in theaccompanying drawings, in which:

FIG. 1 is a perspective view taken from above the plate input end of theapparatus, and looking toward the discharge end thereof;

FIG. 2 is a sectional view taken along line 22 of FIG. 1;

FIG. -3 is a sectional view corresponding to FIG. 2, but taken alongline 3-3 of FIG. 1, and showing a relationship of parts not shown inFIG. 2, as well as omitting certain other parts;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 1, showing therubbing carriage for the developer station on enlarged scale, and withportions broken away to reveal the relationship of driving parts;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4, and showingthe gear system for driving the cluster of rubbing members in rotation;

FIG. 6 is a perspective view showing the bottom or plate-engagingsurface of one of the rubbing members shown in FIG. 4;

FIG. 7 is a perspective view showing the same rubbing member illustratedin FIG. 6 from the upper or mechanically connecting surface thereof;

FIG. 8 is a detail view inside elevation, showing the link of the drivechain for the rubbing carriage which is equipped with the means fortransmitting reciprocatory force to the rubbing carriage;

FIG. 9 is a perspective view showing the storage and distributionsystems for the developer composition and the preservative composition;

FIG. 10 is a top plan view of the apparatus shown in FIG. 1, with therubbing carriage in a different position; and

FIG. 1 1 is a sectional view taken along line 1l11 of FIG. 10.

FIG. 12 is a sectional view of the preservative station of FIG. 2 with arotatable rubbing member.

The embodiment illustrated in the drawings includes an endless belt 1,the front loop of which is trained about a roller 2, and the rear loopof which is trained about a roller 3. An adjustable tension roller (notshown) can be provided on the lower reach of the belt.

An exposed lithographic plate to be treated is fed into the apparatusadjacent roller 2, and transported on the upper reach of belt 1 towardroller 3. The roller 3 is, in the embodiment shown, a drive roll, whilethe roller 2 is an idler roll, so that the upper reach of the belt movesfrom the roller 2 toward the roller 3, and is constantly tensioned inthe direction of its movement to, through, and beyond, a superimposedidler roll 4, a developing station 5, a washing station 6, apreservative station 7, and a squeegee roll 8, all as indicated in FIG.1.

At the developing station 5, there is provided a carriage 9, which isdriven in reciprocation to translate transversely of the direction ofthe movement of the upper reach of belt 1. The carriage is mounted uponspaced trunnions l0 and 11, which guide it during the aforesaidreciprocatory translation; and the carriage is driven in suchreciprocatory translation by an endless chain 12 threaded about an idlersprocket 13 and a driven sprocket 14. The sprockets 13 and 14 aremounted forrotation about shafts supported by crossbar 15, from whichthere projects radially a bracket 16 for mounting a motor 17. The motor17 drives shaft 18 (and sprocket l4 fixedly mounted on that shaft) inrotation which may be either clockwise or counterclockwise, but isalways in the same direction.

'II-Ie trunnion 10 has its opposite ends mounted respectively in links19 and 20, while the opposite ends of said links are hinged on trunnion11, which is permanently mounted to opposite pedestals 21 and 22, whichare in turn securely mounted upon the side frames of a table 23 whichsubtends the developing station portion of the upper reach of belt 1. Acomparable pair of pedestals 24 and 25 support the front ends of links19 and 20, and may be provided with any suitable means 124 and forreleasably latching or detenting such front ends, and the interveningtrunnion 10, in the operating position shown in FIG. 1. The hinging ofthe parts for limited rotation about trunnion 11 serves no function inthe operation of the apparatus, but does facilitate the removal andreplacement of expendable parts of a rubbing assembly mounted upon andmovable with carriage 9, later to be described. Since motor 17 is a partof the thus hingedly mounted assembly, the motor is preferably equippedwith a mercury switch, or other tilt-sensitive device, to automaticallydisconnect the source when the hingedly mounted assembly is moved out ofthe position shown in FIG. 1 and toward the position shown in dottedlines in FIG. 3.

An electric motor 26, having a drive shaft 27 projecting axiallydownward, is mounted upon carriage 9, andits shaft 27 is equipped with apinion 28 which engages a gear 29 and drives the same in rotation. Gear29 is one of a cluster of four identical gears 29, 30, 31 and 32, whichintermesh with each other, as shown in fig. 5, so that alternate ones ofthe cluster rotate in opposite directions about their respective shafts.

The lower end of each gear shaft projects beneath carriage 9, and hasremovably mounted thereon a rubbing member 33 of which there are four inthe embodiment shown. As clearly shown in FIGS. 6 and 7, each rubbingmember is preferably composed of a slab 34 of coarse grain cellulosesponge, or other comparable material, secured to a metal plate 35. Theobverse and reverse faces of the rubbing members are shown in FIGS. 6and 7, respectively; the obverse face being the one which makes rubbingengagement with a plate undergoing treatment; and the metal plate beingthe reverse face. In the form shown, the rubbing members are of circularperiphery, but other curvilinear or polygonal shapes may be employed.The obverse face of each such rubbing member has a central aperture 36which is preferably acircular, and shown as rectangular. Such a centralaperture accomplishes a dual function: first, it accommodates partswhich project downwardly from discs 37 (one of which is fixedly mountedon each of the shafts for gears 29-32) through keyways 38 in mountingplate 35 for snapon connection with the respective rubbing members 33,and provides access to retaining screws therefor; and second, ifacircular, it tends to keep in motion any developer composition whichmay accumulate therein and thereby minimize caking thereof withresultant shortradius streaking of a lithographic plate undergoingtreatment.

The reciprocatory traversing movement of carriage 9 and its adjunctparts transversely of the motion of belt 1 (and transversely of alithographic plate moving with the belt) is accomplished withoutreversing the direction of rotation of drive sprocket 14, or thedirection of movement of chain 12 about its orbit by means now to bedescribed. The drive chain 12 is a common link and roller, or link andblock, endless chain. In such a chain, opposite links 39 are connectedby a common pin 40 either to preceding and succeeding links, or toadjacent blocks. The invention contemplates that one such pin in thechain be equipped with a round-ended cylindrical projection or follower41 at one side of the chain, and with a ball bearing projection orfollower 42 at the other side of the chain. The follower members 41 and42 project sidewardly from the chain in opposite directions, as shown inFIG. 8. The parts 41 and 42 are thus free to rotate about the axis ofpin 40, and may, if desired, be separated from links 39 by nylon washers43 and 44. The driving force for carriage 9 is transmitted from chain 12through the single pin 40 of the chain which has bearing members 41 and42 associated with it. The transverse components of the motion of pin 40are transmitted to the carriage through a C-shaped yoke 45, shown inFIG. 4. The yoke 45 is permanently affixed to carriage 9, and moves withit in translatory reciprocation horizontally at right angles to thedirection of movement of the belt 1. For confining, yet accommodatingvertical movement of, bearing member 41 at the end loops of chain 12,the yoke 45 is provided with a raceway 46 in the continuous side of theC-shaped yoke, and likewise the bearing member 42 is movably confined inopposite discontinuous, but vertically aligned, raceways 47 and 48 inthe discontinuous side of the yoke. These raceways are cross-sectionallycontoured to be substantially contrageneric with the cross-sections ofbearing members 41 and 42, respectively, and to accommodate said bearingmembers for free running vertical movement while held captive therein,as pin 40 of the chain changes direction at either sprocket, 13 or 14,from the upper chord of chain 12 to the lower chord thereof, or viceversa. To facilitate the installation and caging of the ball extensions41 and 42 in the raceways, the yoke 45 may have a separable part 145which constitutes both the top bar of the C shape and the upperdependent in which raceway 47 is located.

Upon the carriage 9, there is also mounted a metering device 49 fordelivering measured quantities of developer composition, and depositingit, either as a continuous stream or drop by drop at spaced intervals,on a subjacent lithographic plate 50 at a position immediately ahead ofthe rubbing members. While economy of developer composition may beeflec'ted by the drop-by-drop technique, the continuous stream techniqueis preferred for assurance of quality. In any event, the developercomposition is preferably deposited on a subjacent plate at a positionwhich will cause each increment to be caught in the bight between theleading pair of rubbing members 33 and 33', as seen in FIG. 10. At thisposition, each member of the leading pair of rubbing members 33 and 33'(when rotating as shown in FIG. 10) has its increments adjacent thebight moving toward each other and generally rearward, i.e., in thedirection of movement of the belt 1. Accordingly, such increments of sodeposited developer, as are not smeared on the plate by the leading pairof rubbing members, are cast toward the trailing pair of rubbing membersand are either smeared on the plate by them, or cast back toward theleading pair.

The metering device 49 is supplied with developer from a tank 51 whichcan be arranged at any convenient place about the apparatus, but, forclarity of illustration, is shown mounted upon a stationary part of theapparatus over the washing station, but it will be understood that thetank can be mounted upon, and movable with, carriage 9, if desired. Thetank 51 has a discharge line 52 extending to a pump 53 which dischargesthrough a line 54 to a T 55, one side of which leads to a T 56, onebranch 57 of which returns to tank 51 and terminates with a fixedrestrictive orifice located within the tank; and the other branch 58 ofwhich extends to a flexible tube 59 leading to the developer meteringdevice 49, as shown in FIG. 1. In order to prevent the flexible tube 59from becoming entangled with adjacent parts during the translatoryreciprocation of carriage 9, the flexible tube 59, which conductsdeveloper composition to metering device 49, and the electricalconductors 60, which control operation of the metering device 49, areeach mounted upon a spring strip 61 pivotally secured at one end 62 tochannel 15, and pivotally secured at the other end 63 to carriage 9. Thespring'strip 61 may be formed of stainless steel having a thickness(e.'g., 0.020 inch) such that it is readily bowed in the thicknessdirection without exceeding its elastic limit, a width sufficient (suchas 1 inch or more) to make it relatively stiff and resistant to bendingin the widthwise direction under the load which it is required tosustain, and of a length sufficient to reach from the pivotal connection62 to pivotal connection 63 when the carriage 9 is at either extreme ofits stroke, but when the carriage is intermediate the ends of itsstroke, the strip 61 bows as shown in FIG. 1. The tube 59, as well aselectrical conductors 60, are anchored to the spring strip 61 not onlyat the ends of the latter, but at at least one intermediate position,and the security of such anchorage is preferably such as to preventcreepage of either tube 59 or conductors 60 relative to the spring stripduring repeated bowing and straightening of the strip.

In the embodiment shown, the metering device 49 is controlledelectrically to open and close a valve therein at predeterminedintervals, as, for example, the time interval required for the carriageto move 4 to 6 inches. While the tank 51 may be covered, in thearrangement shown, it is open to the atmosphere, and in order to assurethe existence of necessary pressure on the developer composition inflexible tube 59 as and when the valve in metering device 49 opens,means is provided for causing the liquid developer in pipe 56 topreferentially flow through branch 58 and tube 59. Such means maycomprise a constriction in branch 57, or making the entire branch 57 ofsmaller bore than branch 58 and tube 59, or providing a valve in branch57 which automatically closes when the valve in metering device 49opens. Alternatively, especially when the developer is thixotropic, thebranch 57 may be replaced by a return .line from metering device 49 totank 51, so that there is a continuous flow of developer past the inletorifice for metering device 49. In either event, the continuous movementof developer from tank 51 through pump 53 and back to tank 51 maintainsthe developer liquid in well-agitated condition, but when thixotropicdeveloper is employed, the aforesaid alternative prevents such increasein its viscosity that supply to metering device 49 is impeded.

For the purpose of ready removal of residual developer composition fromtank 51, as at shut-down of the apparatus at the end of a day, T 55 isalso connected to a line 64 controlled by a valve ,65, which leads to aflexible tube 66 whose open end is situated at a convenient place forcapturing the developer discharged therethrough. Under operatingconditions, however, valve 65 is closed.

For convenience in removing and replacing the rubbing members 33 whichare expendable, the entire carriage 9 and its associated parts,including trunnion 10, chain 12, sprockets 13 and 14, motor 17, and thespring strip 61, is mounted for hinging about trunnion l l (as shown inbroken lines in FIG. 3) to an extent sufficient to enable the rubbingmembers 33 to be readily accessible.

At the washing station 6, there is provided an inverted trough 67 withinwhich there is housed a water header having a series of transverselyspaced nozzles 68 for spraying wate'r downwardly and away from themanner comparable to the reciprocation of metering device 49, butotherwise, it suffices to provide metering devices 70 permanentlylocated in spaced relation 8 to 10 inches apart transversely (widthwise)of the belt 1.

Metering device 70 is supplied with preservative composition from a tank71 which, as shown in FIG. 9, is equipped with a pump 72, whichdischarges into a tee 73, one leg of which extends to tube 74 leading tometering devices 70. As in the case with metering device 49, meteringdevices 70 are electrically controlled to regulate the time intervalbetween successive discharges, and they may, if desired, have a mastercontrol which deactivates all of them save when a plate is presenttherebeneath. The other leg of T 73 is connected to a pipe 75 having avalve 76, which is closed during normal operation of the apparatus, but,as in the case of the developer, may be opened to drain tank 71 atshut-down. While the nature of the preservative composition is usuallynot such as to require continu 1 ous agitation during operation, wherethe preservative developing station, upon subjacent increments of plate50 as they pass beneath the trough 67. Suchrinses away the hydrophiliccomponents of the developer which have not become adhered to thenow-hardened lacquer-forming components of the developer. While normallythe volume of water so sprayed is insufficient, particularly when thebelt is moving to tend to flow backward toward the developing station,the entire apparatus may be tilted slightly to eliminate any suchtendency. As shown, however, the table 23 terminates short of thewashing station so that there is no supporting member in contact withthe lower side of the upper reach of belt within the washing station.This has the two-fold effect of reducing the mechanical drag on thebelt, and of facilitating the elimination of washing water withoutback-flow into the developing station.

At the rear end of the washing station, there is provided a squeegeewhich, in the form shown, is a rubber lip 69 biased into contiguity withthe upper reach of belt 1, and consequently when a plate, such as 50,moves therebeneath on the belt, the rubber lip 69 flexes slightly towipe all flowable water from a plate as it passes. The thus removedwater flows over the edges of belt 1 and is caught by sink 85, shown inFIG. 2. Preferably, the squeegee 69 engages the upper surface of belt 1at a position where the belt is supported as by table 230 which alsosustains the load of rubbing under pressure at the preservative station7.

The preservative station 7 is immediately behind the squeegee devicejust mentioned. At station 7, there is provided one or more meteringdevices 70 for depositing metered increments of a preservativecomposition upon a subjacent plate. While, in the embodiment shown, themetering device 70 is stationary, it will be understood that, ifdesired, it can be reciprocated in a composition does require it, line74 may be provided with a branch leading back to tank 71, as in the caseof the developer system.

At the preservative station 7, and immediately behind the meteringdevice 70, there is also provided means for rubbing the preservativecomposition and spreading it throughout the length and breadth of asubjacent plate. Such a device may, if desired, be in the form of areciprocating carriage comparable to carriage 9, and in such case, themetering device may be mounted upon, and movable with, such a carriage,but need not embody a gang of rubbing members, as one will suffice.However, in the embodiment shown in the drawings, the rubbing means ismounted upon an arm 78 having a boss 79 encircling trunnion 11 (for bothsliding movement axially of, and rotational movement about, trunnion l land restrained against movement relative to the carriage 9 in thedirection of the latters reciprocation. Thus, the bar 78 reciprocateswith the carriage 9, but may be hinged relative to the carriage 9 abouttrunnion 11 as an axis when the carriage and adjunct structure aretilted to the position shown in dotted lines in FIG. 3, or the arm 78may be independently tilted in the counterclockwise direction from theposition shown in FIG. 2. As clearly shown in FIGS. 2 and 10, the arm 78projects rearwardly from trunnion 11 over the washing station 6 and intothe preservative station 7, so that its free end can support a rubbingmember for operation upon a lithographic plate at the preservativestation. Two forms of rubbing member are illustrated in the drawings. Inthe form illustrated in FIGS. 2 and 10, a single rubbing member 77, ofthe same material as rubbing members 33, but of length (widthwise of thebelt) approximately equal to twice the diameter of a rubbing member 33,is fixedly mounted upon the rearward extremity of arm 78. Hence, therubbing member 77 is reciprocated in translation concurrently withcarriage 9, and the rubbing member is so disposed that its stroke(widthwise of the belt) in such reciprocation is equal to that of theleading pair of rubbing members 33 and 33' on carriage 9. Thus, therubbing member 77 operates upon a subjacent plate with compound relativemotion consisting of the component which is moving the plate lengthwiseof the belt 1, and the component which is moving the bers 33. Therotatably rubbing member 770 is mounted on the lower end of a shaft 771,retained in a bearing block 772, which is secured to the free end of arm78. Shaft 771 has affixed to it a pinion 773 which engages a fixed rack774 extending transversely of the apparatus, and mounted upon astationary bar 90, as shown in FIG. 3.

Immediately after emerging from the ambit of rubbing member 77, theleading edge of a plate, such as 50, enters the nip between idler roll 8and belt 1, and as the belt 1 makes the turn about drive roll 3, theplate which has been operated upon is peeled from the belt and deliveredto a discharge apron 80. While the roll 8 may be spring biased towardthe belt, such is likely to permanently deform the surface of roll 8when the apparatus is idle, as over a long weekend, unless some means isprovided to automatically release the bias when the apparatus is idle. Asimpler safeguard against such deformation is to mount one end of roll 8with a fixed nip as shown in FIG. 1, while the other end is providedwith a suitable quick-release mechanism 108 as shown in FIGS. 2 and 3.

A receiving apron 81 is arranged at the front end of the apparatus toguide a plate to be treated into the nip between idler roll 4 and belt1, and apron 81 is equipped with a plate sensor 82 which is the operatorof an electric switch, and so disposed that the switch is normally open,but when a plate passes thereunder, the switch is closed to initiate, inpredetermined sequence, the energization of a plurality of electricalcircuits which respectively control motors 17, 26, and pumps 53 and 72,as well as metering devices 49 and 70; movement of the belt 1 beingsimilarly controlled and so interlocked with the plate sensor 82 thatthe latter will not initiate the energization of any circuit unless thebelt is running.

Since relative movement, between the belt 1 and a lithographic platebeing transported by it, is restrained only by surface tension whichrequires substantial exclusion of air from the belt-plate interface, itis important that the belt 1 be sufficiently wet with liquid to assuresuch exclusion of air from the interface that the plate adheres to thebelt with sufficient tenacity to prevent its movement relative to thebelt while being operated upon by the rubbing members. Hence, means forwetting the belt prior to reaching its loop about idler roll 2 isprovided. In the embodiment shown, such a means comprises a water sprayhead 83 situated below the lower reach of belt 1, and disposed to directa spray of water upwardly onto the lower surface of the lower reach ofbelt 1 for the full width thereof. In order to assure that there is noflowable liquid on the belt as it passes under idler roll 4, a squeegeedevice 84, shown in the form of a wiping blade in FIGS. 2 and 3, isprovided for surface engagement with the belt as it makes the turn aboutidler r0112. Thus, when an increment of belt 1 comes into contact withthe inactive surface of a lithographic plate being fed through the nipbetween idler roll 4 and belt 1, the belt is damp at least to the extentthat whatever pores may be in the belt are filled with liquid, and thereis at least a monomolecular film of liquid on the surface of the belt,but there is substantially no flowable or unsorbed water on the surfaceof the belt. This precaution has a two-foldeffect: first, it minimizesthe transfer of water from belt 1 to idler roll 4 when idler roll 4 isrunning in contact with the belt, i.e., with no plate intervening; andsecond, it minimizes the likelihood that liquid will be squirted out ofthe interface between a plate and the belt at the developing stationwhen the plate is being squeezed between rubbing members 33 and thebelt. While, in the embodiment shown, the belt is pre-wet with water, itwill be understood that other liquids can be used for this purpose. Withthe arrangement shown, water is discharged above the belt at station 6and drains into collector sink 85, which also receives the drippingsfrom the lower reach of belt 1, aswell as the excess discharged by sprayhead 83 and the drippings from squeegee member 84.

In situations where it is desired to stack the processed lithographicplates one upon the other immediately as they emerge on to dischargeapron 80, it is desirable to completely drythem before they are stackedone upon the other, and accordingly the discharge apron may be equippedwith any suitable drying apparatus, such as one which directs a streamof warm, dry air against the emerging plate, and before it is stacked.Since, in accordance with the present invention, a plate, such as 50,being processed in the apparatus is held fast on the belt 1 by virtue ofmoisture at the interface, it is of particular importance to dry thelower surface of any such plate which is to be stacked upon anotherbecause the moisture on the inactive surface of a plate is moredetrimental to the active surface of the plate next below it in thestack than is residual moisture in the active surface of the lowerplate. Accordingly, the invention contemplates the provision of a warmair duct 86 for conducting a stream of warm, dry air from a suitablesource, and directing it through a series of louvers 87 in dischargeapron 80, so as to impinge the warm air against the inactive surface(which has been in contact with belt 1) of a processed lithographicplate as it passes over the louvers 87.

For features of the apparatus which are not specifically describedherein such as the character and speed of the belt 1, the mode ofsecuring the lithographic plate against movement relative to the belt,automatic control of discharges, and the material of which the rubbingmembers may be formed, reference may be had to the aforesaid applicationof Harrel et al.

In the operation of the device, it is preferred that movement of thebelt and release of water from spray head 83 be initiated first topre-condition the belt for the reception of a plate. After the belt hasmoved for a distance sufficient to bring the leading increment, wet byspray head 83, to the nip between idler roll 4 and the belt, an exposedlithographic plate is moved across apron 81 into contact with sensor 82,whereupon the motors l7 and 26 and developer pump 53 begin to operate.Thereafter, within an increment of time no greater than that sufficientto bring the leading edge of the plate into position between the beltand the leading pair of rubbing members 33 and 33, metering device 49 isenergized to release a charge of developer com position nearthe leadingedge of the incoming plate; within an increment of time no greater thanthat sufficient to enable the leading edge of the plate to reach washingstation 6, the supply of water to header 68 is opened; and within nogreater than the increment of time required for the leading edge of theplate to reach preservative station 7, pump 72 and metering device 70are energized. In the embodiment shown, all these devices remainenergized, at least periodically, until movement of belt 1 is stopped,but it will be understood that appropriate devices sensing the presenceor absence of a plate on the belt, subjacent the devices operatingthereon at the successive stations 5, 6 and 7, may be provided fordiscontinuing the operation of such devices sequentially when there isno plate to be operated upon by them respectively. Absent suchplate-present sensors in the respective stations, means which isadjustable in accordance with the dimension (in the direction ofmovement of the belt) of the plate may be provided for automaticallydiscontinuing the operation of the devices at the respective stations.

At developer station 5, increments of developer are dropped on asubjacent plate throughout the reciprocatory stroke of carriage 9 inboth directions, and concurrently rubbed over and into the activesurface of the plate. Preferably, the speed of reciprocation of thecarriage 9 is so coordinated with the speed of belt 1 that any givenincrement of plate is operated upon by at least two of the rubbingmembers 33 during each halfcycle of reciprocation, but where speed ofthe operation is more important than quality of the development, it issufficient that each increment of the plate be operated upon by at leastone of the rubbing members during a whole cycle of reciprocation. Ineither event, during a full cycle of reciprocation of the carriage 9,the path of a given rubbing member on a lithographic plate undergoingtreaunent on the moving belt is V shaped, or half W shaped, dependingupon the position chosen for the beginning of the cycle; and to achieveoptimum results with the form of apparatus shown, the speed of belt 1 isso coordinated with the speed of the carriages reciprocation that thebelt moves no more than a radius of a rubbing member 33 during acomplete cycle of reciprocation; but to decrease the time required forthe entire operation, more rubbing members may be added to the clusterthereof on thecarriage 9, and the speed of the belt increasedaccordingly. Where, as shown in FIG. 10, the width (i.e., parallel withtrunnions 10 and 11) of the belt 1 is sufficiently less than the length(i.e., parallel with trunnions l0 and 11) of the stroke of carriage 9 issuch that at least half the surface of the lefthand pair of rubbingmembers (33 and the one behind it) overreach the lefthand edge of thebelt at the lefthand extremity of the reciprocatory stroke, andconversely at least half the area of the righthand pair of rubbingmembers (33 and the one behind it) overreach the right edge of belt 1 atthe right extremity of the reciprocatory stroke. Since the rubbingmembers are resilient and, when in contact with a plate or the belt,

are under some compression, the increments thereof which overhang theedge of the belt at the respective ends of the reciprocatory strokemomentarily expend as they leave the belt, but are recompressed when, nomore than of rotation later, the re-encounter the edge of the belt.Hence, the edge of the belt serves as a squeegee member to remove anyexcess of developer as the momentarily expended increments of therubbing member are re-compressed upon emerging from a zone at whichtheir compression was released into a zone wherein their compression isresumed. This, together with the feature of discharging the developercomposition from the reciprocatory carriage, at spaced intervals duringits strokes, effects improved utilization of the developer composition,and spreads it uniformly thin so that evaporation of its volatilecomponents is accelerated which latter is further induced by the airturbulence induced by the rotating, counter-rotating, rubbing members.

Because of the compound rubbing motion involved, the construction andmode of operation of the cluster of rubbing members on carriage 9 isideal for the postexposure treatment of lithographic plates, not onlywith developer composition, but also with preservative. The compoundrelative motion between a lithographic plate undergoing treatment andthe cluster of rubbing members involves a number of components;longitudinal rectilinear motion in the direction of the single-headedstraight arrow in FIG. 10; transverse rectilinear motion back and forthin the directions indicated by the double-headed straight arrow in FIG.10; curvilinear motion in the clockwise direction by half the rubbingmembers in the cluster; and curvilinear motion in the counterclockwisedirection by the other half of the rubbing members in the cluster. Agiven increment of a lithographic plate undergoing treatment issubjected to at least three of those motions concurrently; and within agiven half-cycle (indeed, within a fractional part of each stroke, whichamounts to a maximum of slightly more than the diameter of a rubbingmember 33) of the carriages reciprocation, such increment of the plateis subjected to all four of those motions. Not onlyis the character ofthe relative motion variegated, but the speed thereof is variegatedinsofar as concerns the rotation of the rubbing members because therelative speed between a point on a lithographic plate momentarilysituated near the periphery of a rubbing member 33 is greater than therelative speed at that same point on the plate when it assumes alocation nearer the center of rotation of a given rubbing member.

In contrast with the variegated rubbing action which takes place at thedeveloping station, that which takes place at the preservative stationis not necessarily variegated to the same degree. While, in the formshown in FIG. 2, the rubbing action at the preservative station involvesonly a compounding of longitudinal and transverse rectilinear motions,there are certain preservative compositions which perform better ifrubbed in a manner comparable with, but not necessarily in the degreeof, the rubbing action which takes place at the developing station; andaccordingly it is contemplated that where such is necessary, therectilinearly reciprocating rubbing member 77 at the preservativestation be replaced with one, of the character shown in FIG. 12, whichrotates while reciprocating, clockwise in one-half cycle ofreciprocation and counterclockwise in the other half-cycle ofreciprocation. Whether the rubbing member at the preservative station isor is not rotating, the mounting of it with freedom for verticalmovement enables its own weight to impose pressure on the plate beingrubbed, and such pressure can be varied by adding to or subtracting fromthe dead weight of the rubbing assembly.

While one complete embodiment of the invention has been illustrated inthe accompanying drawings, and has been described hereinbefore, savewith respect to some details which are common to the disclosure of theaforesaid application of Harrell et al; and while certain modificationsand variations in the apparatus shown in the drawings have beenhereinbefore indicated, it is not to be understood that the invention islimited to the specifics of the foregoing disclosure. From the foregoingdescription, those skilled in the art will readily understand thestructure, function and mode of operation of the invention, and realizethat it accomplishes its objectives efficiently, expeditiously, andeconomically.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:

1. Apparatus for developing lithographic plates comprising a movingendless belt having a substantially horizontal upper reach, said upperreach supporting and transporting an exposed lithographic plate to,through and beyond a succession of operating stations located along saidreach, a carriage mounted for reciprocation above said upper reachtransversely with respect to said upper reach from adjacent one sidethereof to the other, at least one rubbing member mounted on saidcarriage for reciprocation therewith back and forth across said upperreach, said rubbing member having an active surface disposed forengagement with a subjacent lithographic plate traveling on said upperreach, means mounting said rubbing member for rotation relative to thecarriage about an axis substantially perpendicular to said upper reach,means for driving said carriage in reciprocation back and forthtransversely across said upper reach, and means for rotating saidrubbing member on its said axis as the carriage reciprocates back andforth.

2. The combination of claim 1 in which there is a cluster of rubbingmembers rotatably mounted on said carriage, and said last-mentionedmeans rotates different members of said cluster in opposite senses.

3. The combination of claim 1 in which said means for driving saidcarriage is an endless chain, a pair of spaced sprockets engaging saidendless chain to confine the path thereof to spaced chords between thesprockets and end loops at the sprockets, and forcetransmitting meansinterconnecting said .chain with said carriage to reciprocate the latterwhile the chain moves continuously in the same sense about its path.

4. The combination of claim 1 having metering means on the carriage fordropping measured charges of developer composition on a lithographicplate being transported by said upper reach before the plate reachessaid rubbing member.

5. The combination of claim 4 having a stationary developer supply tank,means connecting said supply tank with said metering means including aflexible tube for conducting developer fluid to said metering means,

and means relatively flexible in the horizontal direction but relativelystiff in the vertical direction for supporting said flexible tubeadjacent the carriage and following movement of the carriage duringreciprocation.

6. Apparatus for developing lithographic plates comprising a movingendless belt having a substantially horizontal upper reach, said upperreach supporting and transporting an exposed lithographic plate to,through and beyond a succession of operating stations located along saidreach, a carriage mounted for reciprocation above said upper reach, arubbing member rotatably mounted on said carriage, said rubbing memberhaving an active surface disposed for engagement with a subjacentlithographic plate traveling on said upper reach, means for driving saidcarriage in reciprocation in directions transverse to the movement ofsaid upper reach, and means for imparting arcuate motion to said rubbingmember, said means for driving the carriage comprising an endless chain,a pair of spaced sprockets engaging said endless chain to confine thepath thereof to spaced chords between the sprockets and end loops at thesprockets, and forcetransmitting means interconnecting said chain withsaid carriage to reciprocate the latter while the chain movescontinuously in the same sense about its path, wherein saidforce-transmitting means includes: a follower mounted on and projectingfrom one of said carriage and said chain; and raceway means on the otherof said carriage and said chain, said raceway means accommodating saidfollower and transmitting force therebetween throughout the path of saidchain.

7. The combination of claim 6 wherein: the follower is affixed to thechain and has a rotatable bearing member disposed outwardly of the chainon at least one side thereof; and said raceway is affixed to thecarriage, extends in the direction parallel with the interspace betweensaid chain chords, and is contoured to be substantially contragenen'c,but have a free-running fit, with said bearing member as the lattermoves about the loops of said path.

8. Apparatus for developing lithographic plates comprising a movingendless belt having a substantially horizontal upper reach, said upperreach supporting and transporting an exposed lithographic plate to,through and beyond a succession of operating stations located along saidreach, a carriage mounted for reciprocation above said upper reach, arubbing member rotatably mounted on said carriage, said rubbing memberhaving an active surface disposed for engagement with a subjacentlithographic plate traveling on said upper reach, means for driving saidcarriage in reciprocation in directions transverse to the movement ofsaid upper reach, and means for imparting arcuate motion to said rubbingmember, metering means on the carriage for dropping measured charges ofdeveloper composition on a lithographic plate being transported by saidupper reach before the plate reaches said rubbing member, a stationarydeveloper supply tank, means connecting said supply tank with saidmetering means including a flexible tube for conducting developer fluidto said metering means, and means relatively flexible in the horizontaldirection but relatively stiff in the vertical direction for supportingsaid flexible tube adjacent the carriage and following movement of thecarriage during reciprocation,

17 wherein said last-named means having:

a. resiliency sufficient to withstand repeated bowing about an arc whoseradii are substantially parallel with the thickness of said strip; and

b. stiffness sufficient to resist bowing about an arc whose radii aresubstantially parallel with the width of said strip;

said strip being substantially wider than it is thick, and substantiallylonger than it is wide, means connecting one end of said strip to astationary member, hinge means connecting the other end of said strip tosaid carriage, and the length of said strip being at least about halfthe reciprocating stroke of said hinge means. 9. Apparatus fordeveloping lithographic plates comprising a moving endless belt having asubstantially horizontal upper reach, said upper reach supporting andtransporting an exposed lithographic plate to,

is a strip of material traveling in one direction transversely acrosssaid path and another reach traveling in the opposite direction throughand beyond a succession of operating stations located along said reach,a carriage mounted for reciprocation above said upper reach, a rubbingmember rotatably mounted on said carriage, said rubbing member having anactive surface disposed for engagement with a subjacent lithographicplate traveling on said upper reach, means for driving said carriage inreciprocation in directions transverse to the movement of said upperreach, and means for imparting arcuate motion to said rubbing member,said carriage being entrapped on and movable along parallel spaced guiderails, means connecting said guide rails together at each of their ends,means permanently mounting and holding captive both ends of one of saidguide rails, means releasably mounting both ends of the other guiderail, and said first-mentioned guide rail providing an axis about whichsaid other guide rail and said carriage may be hinged to make saidrubbing member accessible for replacement.

10. Apparatus for developing lithographic plates comprising means forcontinuously conveying an exposed lithographic plate along apredetermined path with the exposed face of the plate facing up, meansfor applying a developer to said face, a carriage mounted forreciprocation above said path and transversely with respect to saidpath, at least one rubbing member for said developer mounted on saidcarriage for reciprocation therewith back and forth across said path,said rubbing member having an active surface disposed for engagementwith a subjacent lithographic plate traveling in said path, meansmounting said rubbing member for rotation relative to the carriage aboutan axis substantially perpendicular to said path, means for driving saidcarriage in reciprocation back and forth transversely across said path,and means for rotating said rubbing member on its said axis as thecarriage reciprocates back and forth.

11. Apparatus as set forth in claim 10 having a plurality of rubbingmembers each mounted on the carriage for rotation relative to thecarriage on an axis substantially perpendicular to said path, saidrubbing member rotating means being carried by the carriage andincluding means for rotating different rubbing members in oppositedirections.

12. Apparatus as set forth in claim 10 wherein said means for drivingthe carriage comprises -an endless chain drive including an endlesschain having a reach transversely across said path, and means forinterconnecting the carriage and said one reach at one end of said chaindrive for moving the carriage in said one direction across said path andfor interconnecting the carriage and said other reach at the other endof said chain drive for moving the carriage in the opposite directionacross said path.

13. Apparatus as set forth in claim 10 having support means extending indownstream direction from said carriage reciprocable with the carriage,metering means for dropping measured charges of preservative compositionon a lithographic plate moving in said path downstream from saidcarriage, and rubbing means carried by said support means fordistributing said preservative over said lithographic plate.

14. Apparatus as set forth in claim 13 wherein said preservative rubbingmeans comprises at least one preservative rubbing member rotatablymounted on said support means, and means for rotatably driving saidpreservative rubbing member.

15. Apparatus as set forth in claim 14 wherein said preservative rubbingmember driving means comprises a stationary rack extending transverselyrelative to said path and a pinion carried by said preservative rubbingmember in mesh with said rack for rotatably driving said preservativerubbing member as it is reciprocated transversely of said path by thecarriage.

16. Apparatus as set forth in claim 10 wherein said carriage drivingmeans drives the carriage back and forth across said path at a speedsubstantially greater than the speed of travel of each plate along saidpath so that said rubbing member contacts substantially the entire areaof said face of each plate as it travels below said rubbing member alongsaid path.

17. Apparatus for developing lithographic plates comprising means forcontinuously conveying an exposed lithographic plate along apredetermined path with the exposed face of the plate facing up, meansat a first location along said path for applying a developer for theplate on to the said exposed upper face of the plate, and means at asecond location along said path for rubbing the developer over the upperface of the plate, said rubbing means comprising a head extendingtransversely with respect to said path across said apparatus above saidpath, sponge means carried by said head for rubbing movement relative tothe head and engageable with the upper face of the plate to rub in thedeveloper, means carried by said head for driving said sponge means toeffect said rubbing movement of the sponge means relative to said head,means for detachably connecting said sponge means to said driving meansfor removal and replacement of said sponge means, and means mountingsaid head for swinging movement between an operative position with thesponge means facing downward for engagement with a plate being conveyedalong said path and a raised position for facilitating removal andreplacement of the sponge means.

18. Apparatus as set forth in claim 17 wherein the said mounting meansfor the head supports the head for swinging movement about an axisextending across said apparatus above said path.

1. Apparatus for developing lithographic plates comprising a movingendless belt having a substantially horizontal upper reach, said upperreach supporting and transporting an exposed lithographic plate to,through and beyond a succession of operating stations located along saidreach, a carriage mounted for reciprocation above said upper reachtransversely with respect to said upper reach from adjacent one sidethereof to the other, at least one rubbing member mounted on saidcarriage for reciprocation therewith back and forth across said upperreach, said rubbing member having an active surface disposed forengagement with a subjacent lithographic plate traveling on said upperreach, means mounting said rubbing member for rotation relative to thecarriage about an axis substantially perpendicular to said upper reach,means for driving said carriage in reciprocation back and forthtransversely across said upper reach, and means for rotating saidrubbing member on its said axis as the carriage reciprocates back andforth.
 2. The combination of claim 1 in which there is a cluster ofrubbing members rotatably mounted on said carriage, and saidlast-mentioned means rotates different members of said cluster inopposite senses.
 3. The combination of claim 1 in which said means fordriving said carriage is an endless chain, a pair of spaced sprocketsengaging said endless chain to confine the path thereof to spaced chordsbetween the sprockets and end loops at the sprockets, andforce-transmitting means interconnecting said chain with said carriageto reciprocate the latTer while the chain moves continuously in the samesense about its path.
 4. The combination of claim 1 having meteringmeans on the carriage for dropping measured charges of developercomposition on a lithographic plate being transported by said upperreach before the plate reaches said rubbing member.
 5. The combinationof claim 4 having a stationary developer supply tank, means connectingsaid supply tank with said metering means including a flexible tube forconducting developer fluid to said metering means, and means relativelyflexible in the horizontal direction but relatively stiff in thevertical direction for supporting said flexible tube adjacent thecarriage and following movement of the carriage during reciprocation. 6.Apparatus for developing lithographic plates comprising a moving endlessbelt having a substantially horizontal upper reach, said upper reachsupporting and transporting an exposed lithographic plate to, throughand beyond a succession of operating stations located along said reach,a carriage mounted for reciprocation above said upper reach, a rubbingmember rotatably mounted on said carriage, said rubbing member having anactive surface disposed for engagement with a subjacent lithographicplate traveling on said upper reach, means for driving said carriage inreciprocation in directions transverse to the movement of said upperreach, and means for imparting arcuate motion to said rubbing member,said means for driving the carriage comprising an endless chain, a pairof spaced sprockets engaging said endless chain to confine the paththereof to spaced chords between the sprockets and end loops at thesprockets, and force-transmitting means interconnecting said chain withsaid carriage to reciprocate the latter while the chain movescontinuously in the same sense about its path, wherein saidforce-transmitting means includes: a follower mounted on and projectingfrom one of said carriage and said chain; and raceway means on the otherof said carriage and said chain, said raceway means accommodating saidfollower and transmitting force therebetween throughout the path of saidchain.
 7. The combination of claim 6 wherein: the follower is affixed tothe chain and has a rotatable bearing member disposed outwardly of thechain on at least one side thereof; and said raceway is affixed to thecarriage, extends in the direction parallel with the interspace betweensaid chain chords, and is contoured to be substantially contrageneric,but have a free-running fit, with said bearing member as the lattermoves about the loops of said path.
 8. Apparatus for developinglithographic plates comprising a moving endless belt having asubstantially horizontal upper reach, said upper reach supporting andtransporting an exposed lithographic plate to, through and beyond asuccession of operating stations located along said reach, a carriagemounted for reciprocation above said upper reach, a rubbing memberrotatably mounted on said carriage, said rubbing member having an activesurface disposed for engagement with a subjacent lithographic platetraveling on said upper reach, means for driving said carriage inreciprocation in directions transverse to the movement of said upperreach, and means for imparting arcuate motion to said rubbing member,metering means on the carriage for dropping measured charges ofdeveloper composition on a lithographic plate being transported by saidupper reach before the plate reaches said rubbing member, a stationarydeveloper supply tank, means connecting said supply tank with saidmetering means including a flexible tube for conducting developer fluidto said metering means, and means relatively flexible in the horizontaldirection but relatively stiff in the vertical direction for supportingsaid flexible tube adjacent the carriage and following movement of thecarriage during reciprocation, wherein said last-named means is a stripof material having: a. resiliency sufficient to withstand repeatedbowing aBout an arc whose radii are substantially parallel with thethickness of said strip; and b. stiffness sufficient to resist bowingabout an arc whose radii are substantially parallel with the width ofsaid strip; said strip being substantially wider than it is thick, andsubstantially longer than it is wide, means connecting one end of saidstrip to a stationary member, hinge means connecting the other end ofsaid strip to said carriage, and the length of said strip being at leastabout half the reciprocating stroke of said hinge means.
 9. Apparatusfor developing lithographic plates comprising a moving endless belthaving a substantially horizontal upper reach, said upper reachsupporting and transporting an exposed lithographic plate to, throughand beyond a succession of operating stations located along said reach,a carriage mounted for reciprocation above said upper reach, a rubbingmember rotatably mounted on said carriage, said rubbing member having anactive surface disposed for engagement with a subjacent lithographicplate traveling on said upper reach, means for driving said carriage inreciprocation in directions transverse to the movement of said upperreach, and means for imparting arcuate motion to said rubbing member,said carriage being entrapped on and movable along parallel spaced guiderails, means connecting said guide rails together at each of their ends,means permanently mounting and holding captive both ends of one of saidguide rails, means releasably mounting both ends of the other guiderail, and said first-mentioned guide rail providing an axis about whichsaid other guide rail and said carriage may be hinged to make saidrubbing member accessible for replacement.
 10. Apparatus for developinglithographic plates comprising means for continuously conveying anexposed lithographic plate along a predetermined path with the exposedface of the plate facing up, means for applying a developer to saidface, a carriage mounted for reciprocation above said path andtransversely with respect to said path, at least one rubbing member forsaid developer mounted on said carriage for reciprocation therewith backand forth across said path, said rubbing member having an active surfacedisposed for engagement with a subjacent lithographic plate traveling insaid path, means mounting said rubbing member for rotation relative tothe carriage about an axis substantially perpendicular to said path,means for driving said carriage in reciprocation back and forthtransversely across said path, and means for rotating said rubbingmember on its said axis as the carriage reciprocates back and forth. 11.Apparatus as set forth in claim 10 having a plurality of rubbing memberseach mounted on the carriage for rotation relative to the carriage on anaxis substantially perpendicular to said path, said rubbing memberrotating means being carried by the carriage and including means forrotating different rubbing members in opposite directions.
 12. Apparatusas set forth in claim 10 wherein said means for driving the carriagecomprises an endless chain drive including an endless chain having areach traveling in one direction transversely across said path andanother reach traveling in the opposite direction transversely acrosssaid path, and means for interconnecting the carriage and said one reachat one end of said chain drive for moving the carriage in said onedirection across said path and for interconnecting the carriage and saidother reach at the other end of said chain drive for moving the carriagein the opposite direction across said path.
 13. Apparatus as set forthin claim 10 having support means extending in downstream direction fromsaid carriage reciprocable with the carriage, metering means fordropping measured charges of preservative composition on a lithographicplate moving in said path downstream from said carriage, and rubbingmeans carried by said support means for distributing said preservativeover said lithographic plate.
 14. Apparatus as set forth in claim 13wherein said preservative rubbing means comprises at least onepreservative rubbing member rotatably mounted on said support means, andmeans for rotatably driving said preservative rubbing member. 15.Apparatus as set forth in claim 14 wherein said preservative rubbingmember driving means comprises a stationary rack extending transverselyrelative to said path and a pinion carried by said preservative rubbingmember in mesh with said rack for rotatably driving said preservativerubbing member as it is reciprocated transversely of said path by thecarriage.
 16. Apparatus as set forth in claim 10 wherein said carriagedriving means drives the carriage back and forth across said path at aspeed substantially greater than the speed of travel of each plate alongsaid path so that said rubbing member contacts substantially the entirearea of said face of each plate as it travels below said rubbing memberalong said path.
 17. Apparatus for developing lithographic platescomprising means for continuously conveying an exposed lithographicplate along a predetermined path with the exposed face of the platefacing up, means at a first location along said path for applying adeveloper for the plate on to the said exposed upper face of the plate,and means at a second location along said path for rubbing the developerover the upper face of the plate, said rubbing means comprising a headextending transversely with respect to said path across said apparatusabove said path, sponge means carried by said head for rubbing movementrelative to the head and engageable with the upper face of the plate torub in the developer, means carried by said head for driving said spongemeans to effect said rubbing movement of the sponge means relative tosaid head, means for detachably connecting said sponge means to saiddriving means for removal and replacement of said sponge means, andmeans mounting said head for swinging movement between an operativeposition with the sponge means facing downward for engagement with aplate being conveyed along said path and a raised position forfacilitating removal and replacement of the sponge means.
 18. Apparatusas set forth in claim 17 wherein the said mounting means for the headsupports the head for swinging movement about an axis extending acrosssaid apparatus above said path.